This invention relates to deposition of magnetic materials. More particularly, the invention relates to an electromagnetic field generator for improved deposition of magnetic materials and a method of operation.
Deposition systems (e.g. ion beam, physical vapor, and evaporation deposition) are capable of depositing high-quality thin films of a wide variety of materials on many different types of substrates. Applications for ferromagnetic thin films, such as deposition of magnetoresistive (MR) and giant magnetoresistive (GMR) films for thin-film magnetic heads, usually require orientation of the magnetic moments in a specific direction by application of an external magnetic field. The required field strength is usually 20-100 Gauss.
It has been found, however, that DC magnetic fields are troublesome for plasma deposition systems due to interactions between the magnetic field and the plasma. Such interactions can, for example, decrease the thickness uniformity of the deposited magnetic film as a result of decreased plasma uniformity. We have also found that magnetic fields in the deposition chamber can adversely affect ion beam deposition processes even at levels as low as 10-15 Gauss due to interactions of the magnetic fields with the ion beam. During ion beam deposition, magnetic field disturbances can cause broadening or displacement of the ion beam which can result in film contamination. Further, the electrons in the ion beam chamber, which normally act to neutralize any charge build-up on the substrate, are very easily trapped by magnetic fields. Such trapping can cause loss of neutralization and subsequent arc damage on any exposed insulating surfaces on the substrate or any electrostatic discharge-sensitive device structures embedded in the substrate wafer, such as magnetoresistive sensors. This is particularly important if an ion-assisted deposition process is used because the assisting ion beam is aimed at the substrate directly.
What is needed is a method of depositing magnetic materials in a deposition system in the presence of an assisting magnetic field without disrupting the source or creating charge build-up on the sample or in the chamber.
In accordance with the present invention, there is described an electromagnetic field generator and method of operation for deposition of magnetic materials. The electromagnetic field generator comprises an open frame electromagnetic assembly having a first pair of spaced apart magnetic members for generating on a substrate a magnetic field in a first direction and a second pair of magnetic members for generating a magnetic field on the substrate in a second direction. Preferably the electromagnetic field generator includes a second electromagnetic assembly spaced apart from the first assembly and magnetically linked to the first assembly to enhance field uniformity on the substrate. The method comprises the steps of: placing a sample within an electromagnetic field generator with at least two selectable magnetic field orientations; operating a source, for example an ion source or plasma source, to deposit material onto the sample influenced by the electromagnetic field generator; and creating a field pattern around the sample with the electromagnetic field generator to control the deposition of the magnetic material.
There are also described various methods for control of deposited materials using different current signals applied to the electromagnetic field generator, with resultant different magnetic fields. The currents include alternating current; positive/negative pulsed direct current; exponentially decaying alternating current; half-wave rectified alternating current; positive-pulsed direct current; positive direct current bias; pulsed direct current with positive direct current bias; and time phased magnetic field and ion generator operation.
An objective is that a combination open frame/base plate electromagnetic field generator provides measured magnetic field directionality within a tolerance of 0.5 degrees over a six inch square substrate or an eight inch circular substrate. This enables deposition of oriented magnetic films with minimal error in directionality.
Another objective is the ability to orient the magnetic field in any arbitrary direction which enables the deposition of alternating layers of differently oriented magnetic films.
Another objective is the ability to continuously change the orientation of the magnetic field in a rotating manner, so as to demagnetize the deposited film.
Another objective is that it provides a uniform magnetic field region over a sample with field uniformity of +/xe2x88x925%.
Another objective is the reduction in weight afforded by the open frame top plate with its truncated corners. The truncated corners also reduce the diagonal clearance required in the chamber to accommodate the field generator. The open frame design also enables the electromagnetic field generator to surround and thus remain clear of the active deposition area; the electromagnetic field generator can thus be shielded from accumulation of sputtered material. This reduces the level of maintenance required to keep the field generator in peak operating condition.
It is not intended that the invention be summarized here in its entirety. Rather, further features, aspects, and advantages of the invention are set forth in or are apparent from the following description and drawings.